AV (Audio Visual) systems connected to various devices such as a television, video, and DVD (Digital Versatile Disc) handling image signals and audio signals have become commonly used in general household.
To establish an AV system, image signals and audio signals have typically been transmitted between devices using coaxial cables and optical fibers. For this reason, physical limitations are imposed on the connection between devices.
However, there is a recently-developed transmission system which can increase the freedom of the connection between devices. In this system, analog signals such as image signals and audio signals are converted to digital signals, and transmitted using packet wireless communication method. A video/sound transmitting system disclosed by Japanese Laid-Open Patent Application No. 10-322670/1998 (Tokukaihei 10-322670) is one of known examples of the above-mentioned transmission system.
However, the aforementioned wireless communication device has such a defection that the more the transmission distance is lengthened, the more the device becomes vulnerable to multipath. phasing, and since the signal degradation caused during the transmission is unavoidable, it is difficult to obtain high-quality outputs. Here, the multipath phasing is briefly explained as below. An outgoing radio wave is typically reflected, scattered, and diffracted by various media, before arriving at a receiving end. Since the reflected wave, scattered wave, and diffracted wave pass through each different path, these waves arrive at the receiving end at each different time. Then the waves are combined with each other in the receiving end, and electric field intensity is determined. On this occasion, the waves may be in phase with each other and hence added up, or may be out of phase and hence cancel each other out. Thus, the electric field intensity fluctuates, in other words, so-called phasing occurs. This is the multipath phasing.
By reason of this signal degradation due to the multipath phasing, an image or sound from the device performing real-time transmission, such as television, is interrupted, if an error still remains at the instant of playback. On this account, users cannot fully enjoy the content to be played.
To solve this problem, for instance, Japanese Laid-Open Patent Application No. 2-39735/1990 (Tokukaihei 2-39735) discloses an antenna diversity method selecting one of a plurality of antennas. In this method, for instance, terminal levels of the respective antennas are compared with each other and an antenna receiving a phasing wave with the highest level is selected.
However, in this conventional method, the received level is determined during a period of a preamble (start code) section which is for synchronizing the reading at the head of a packet, and thus the preamble section has to be sufficiently long in order to switch the antennas so as to select the most suitable antenna by determining the received level in the preamble section. For this reason, to solve this problem, it is necessary for the method to adopt a hardware or high-speed CPU (Central Processing Unit) for high-speed processing.
The present invention has been developed for solving the foregoing problems of conventional arts, thereby aiming at providing a wireless communication device which can improve the quality of signals without adopting a hardware or high-speed CPU for high-speed processing, on the occasion that image and audio signals are transmitted between devices of an AV system through wireless communication.